High-performance liquid chromatographic analysis using a highly sensitive fluorogenic reagent, 2-anthroyl chloride, and stereoselective determination of the enantiomers of mexiletine in human serum

Development and application of a validated HPLC method for the analysis of dissolution samples of mexiletine hydrochloride capsules

The aim of this work was to develop and validate a simple, efficient, sensitive and selective method for the analysis of dissolution samples of mexiletine hydrochloride capsules by HPLC without the necessity of any time-consuming extraction, dilution or evaporation steps prior to drug assay. Separation was performed isocratically on a 5 ?m LiChrospher 60, RP-Select B column (250 x 4 mm ID) using the mobile phase buffer-acetonitrile (60:42, v/v) at a flow rate of 1.2 mL min-1 and UV detection at 262 nm. The elution occurred in less than 10 minutes. The assay was linear in the concentration range 50-300 ?g mL-1 (r2 = 0.9998). The validation characteristics included accuracy, precision, linearity, specificity, limits of detection and quantification, stability, and robustness. Validation acceptance criteria were met in all cases (the percent recoveries ranged between 100.01 and 101.68 %, RSD < 0.44 %). The method could be used for the determination of mexiletine hydrochloride and for monitoring its concentration in in vitro dissolution studies.

Development of a capillary electrophoresis assay for the determination of carvedilol enantiomers in serum using cyclodextrins

A capillary electrophoresis method using cyclodextrins as the chiral selectors was developed for the determination of carvedilol enantiomers in serum. Several types of cyclodextrins were evaluated. The effect of cyclodextrin concentration on enantiomer resolution was investigated. Best results were obtained using 10 mM hydroxypropyl-beta-cyclodextrin in the run buffer. The effect of voltage on efficiency was assessed. Other electrophoretic conditions were optimized. The method was validated for carvedilol enantiomers in serum. Linearity of detection was assessed over the concentration range of 50-4000 ng/ml of each enantiomer in serum. Intra- and inter-assay variability obtained were under 8% for both enantiomers.

Enantioselective determination of the hydroxylated metabolites of mexiletine in human plasma

Pre-column derivatization with o-phthaldialdehyde and N-acetyl-l-cysteine was used for liquid-chromatographic diastereomeric resolution of p-hydroxymexiletine (PHM) and hydroxymethylmexiletine (HMM), metabolites of mexiletine formed by aromatic and aliphatic hydroxylation, respectively. The resulting diastereomeric derivatives were resolved on a C18 column and monitored by fluorescence detection. The diastereomeric elution order for both metabolites was determined on the basis of the circular dichroism spectra of each eluted fraction. Plasma samples (500 microliters) showed recoveries greater than 75% for both the metabolites. Calibration curves in plasma samples were linear over the concentration ranges 10-500 and 20-1,000 ng/ml for each enantiomer of PHM and HMM, respectively. The limits of quantitation were found to be 10.0 and 5.0 ng/ml for both enantiomers of PHM and HMM. The within-day and between-day coefficients of variation were less than 10%. The assay was shown to be suitable for a pharmacokinetic study performed in a patient with ventricular arrhythmias following the short-term oral treatment of 200 mg t.i.d. of racemic mexiletine hydrochloride.

Recent chromatographic and electrophoretic enantioseparations of cardiovascular drugs

The chromatographic and electrophoretic enantiomeric separation and analysis of several clinically used cardiovascular drugs have been reviewed. Several examples of recently reported applications of enantioselective analysis and various cardiovascular agents are presented.

High-performance liquid chromatographic determination of mexiletine enantiomers in plasma using direct and indirect enantioselective separations

Two methods were developed for the determination of mexiletine enantiomers in plasma samples suitable for studies on the stereoselective disposition of this drug. Both methods used fluorescence detection to improve sensitivity and selectivity. The direct enantioselective separation was based on the chiral resolution of mexiletine-2-naphthamide derivatives on a Chiralcel OJ column. The calibration curves were linear over the concentration range 50-500 ng/ml for each enantiomer; therefore the method can be used only for therapeutic monitoring, drug interaction and multiple dose pharmacokinetic studies. The indirect method was based on the formation of diastereomers using o-phthaldialdehyde and N-acetyl-L-cysteine reagents. The diastereomers were resolved on a reversed-phase RP-18 column. The method proved to be suitable for single or multiple dose pharmacokinetic studies based on the low quantification limit (1 ng/ml) and the broader linear range (1-1000 ng/ml) obtained.

Determination of the enantiomeric composition of mexiletine and its four hydroxylated metabolites in urine by enantioselective capillary gas chromatography

The enantiomers of mexiletine and four of its hydroxylated metabolites were directly separated by capillary gas chromatography using a heptakis(6-O-tert-butyl-dimethylsilyl-2,3-di-O-methyl)-beta- cyclodextrin column. The method was applied to the analysis of urine samples from cancer patients who were treated with racemic mexiletine as part of a study of the use of mexiletine in the relief of neuropathic pain. Samples analyzed before and after deconjugation of the urine with beta-glucuronidase/arylsulfatase showed a high stereoselectivity in the formation and conjugation of these compounds.